The present invention relates to a MEMS element including at least one deflectable functional element, which is implemented in a layered structure on a MEMS substrate, so that a space exists between the layered structure and the MEMS substrate, at least in the area of the functional element, and including a stress decoupling structure, which is formed in the MEMS substrate. Furthermore, the present invention relates to a component including such a MEMS element.
MEMS elements may be used, for example, as sensor elements for detecting and measuring accelerations, rotation rates, magnetic fields and pressures for the most varied applications, for example, in the automotive technology and consumer segment. Particular emphasis is placed on miniaturization of the elements and components including high function integration. In this respect, so-called bare die or chip scale packages prove to be particularly advantageous, since repackaging of the chips is omitted in this case. Instead, the MEMS chip is either assembled directly on an application circuit board (bare die) or in the chip stack of a vertically hybrid integrated component (chip scale package).
Due to the direct assembly of the MEMS chip or chip stack as part of the 2nd level assembly, deformations of the application circuit board are very directly coupled into the MEMS element. In this process, stress effects occur, which may severely impair the MEMS function.
The sensitivity to stress of MEMS elements of the type discussed here may be reduced with the aid of a stress decoupling structure in the MEMS substrate. Consequently, MEMS elements having deep trenches in the rear side of the substrate are known. These trenches are placed circumferentially in relation to the deflectable functional element, which is formed in the MEMS layered structure. The extremely thinned segments of the MEMS substrate in the trench area may readily absorb the deformation of a carrier, while the MEMS substrate in the area of the functional element experiences no more than a slight deformation due to its being very thick and stiff in comparison.
However, in practice, the conventional stress decoupling structure proves to be problematic in several respects.
Since the trench structure is applied in the rear side of the substrate, particles may collect in the trench structure during further processing, which may completely cancel the stress decoupling effect or at least significantly reduce it. The local coupling on a single location and a simultaneous leverage effect may even increase the input of stress into the MEMS structure of the functional element. The trench structure may actually be filled with an elastic material in order to prevent an introduction of particles. However, this is invariably associated with a significantly limited stress decoupling effect.
Moreover, the depth of the trench structure in relation to the thickness of the MEMS substrate must be defined very precisely in order to achieve an effective stress decoupling. Depending on the thickness of the MEMS substrate, this is connected with comparatively high technical manufacturing complexity and is accordingly cost-intensive.